From mboxrd@z Thu Jan 1 00:00:00 1970 From: Pekka Enberg Subject: Re: [rfc][patch 1/3] slub: fix small HWCACHE_ALIGN alignment Date: Mon, 03 Mar 2008 23:35:44 +0200 Message-ID: <47CC6F30.50802@cs.helsinki.fi> References: <20080303093449.GA15091@wotan.suse.de> <20080303200613.GC8974@wotan.suse.de> <20080303201701.GF8974@wotan.suse.de> <84144f020803031330i2c0ea1f6kc5b02c8b26145797@mail.gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: Nick Piggin , netdev@vger.kernel.org, Linux Kernel Mailing List , yanmin_zhang@linux.intel.com, David Miller , Eric Dumazet To: Christoph Lameter Return-path: Received: from courier.cs.helsinki.fi ([128.214.9.1]:58732 "EHLO mail.cs.helsinki.fi" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751434AbYCCVhA (ORCPT ); Mon, 3 Mar 2008 16:37:00 -0500 In-Reply-To: Sender: netdev-owner@vger.kernel.org List-ID: Hi, Christoph Lameter wrote: > Well the guarantee can only be exploited if you would check the cacheline > sizes and the object size from the code that creates the slab cache. > Basically you would have to guestimate what the slab allocator is doing. > > So the guarantee is basically meaningless. If the object is larger than a > cacheline then this will never work. Yes, I know that. That's why I am asking why this matters. If there's some sort of regression because SLUB does HWCACHE_ALIGN bit differently, we need to fix that. Not that it necessarily means we have to change HWCACHE_ALIGN but I am assuming Nick has some reason why he wants to introduce the SMP alignment flag. Pekka